Quantitative paleoenvironmental and paleoclimatic reconstruction ...

ARTICLE IN PRESS
2 N.D. Sheldon, N.J. Tabor / Earth-Science Reviews xxx (2009) xxx–xxx
5.5. Paleoprecipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
5.5.1. Content of Fe–Mn nodules in vertisols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
5.5.2. Depth to Bk horizon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
5.5.3. Bw/Bt horizon geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
5.6. Long-term chemical weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6. Thermodynamic approaches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6.1. Simple versus complex systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6.2. Single-equation approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6.2.1. Precambrian atmospheric CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6.2.2. Earliest Triassic soil formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
6.3. Multiple-equation approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7. Stable isotope approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.1. Stableisotopiccompositionofpedogenicmineralsaspaleoenvironmentalproxies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.1.1. Mineral-water isotope fractionation and the jargon of stable isotope geochemistry . . . . . . . . . . . . . . . . . . . . . . . 0
7.1.2. Stable isotope fractionation factors of common pedogenic minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.1.3. Relationship between hydrogen and oxygen isotopes in continental waters . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.2. Carbon in soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.2.1. One-component soil CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.2.2. Two-component soil CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.2.3. Three-component soil CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.3. Soil and paleosol carbonate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.3.1. Pedogenic calcite δ 18 O values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.3.2. Pedogenic siderite as a proxy for soil moisture δ 18 O values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.4. δ 13 C values of soil carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.4.1. Calcite from one-component of soil CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.4.2. δ 13 C of pedogenic siderite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.4.3. Calcite derived from 2-component soil CO 2 mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.4.4. Soil carbonates formed by mixing of three-components of soil CO 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.5. δ 18 O and δD of hydroxylated minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.5.1. Origin of residual deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.5.2. Variations in soil moisture δ 18 O and δD values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.5.3. Single-mineral paleotemperature estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.5.4. Mineral-pair δ 18 O values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
7.6. Paleo-vegetation/paleo-photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
8. Future approaches and challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
8.1. Boron isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
8.2. Energy balance models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
8.3. “Clumped isotope” paleothermometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
9. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
1. Introduction
Increasing recognition of paleosols (fossil soils; Fig. 1) in nonmarine
strata has opened up new types of paleoenvironmental and
paleoclimatic reconstructions. While good quantitative paleoclimatic
data may be obtained from plant fossil assemblages using either
nearest living relative (e.g., Leopold and Clay-Poole, 2001; Utescher
and Mosbrugger, 2007) or leaf morphometric approaches (e.g., Wolfe,
1994; Uhl et al., 2007), those approaches yield snap shots of past
environments and are relatively rare in the fossil record. Paleosols
preserved in continental basins on the other hand, raise the possibility
of long-term, fairly continuous paleoclimatic records, potentially with
a temporal resolution that equals that of marine proxy records (e.g.,
Retallack et al., 2004b; Sheldon and Retallack, 2004; Retallack, 2007).
The last point is crucial because unlike most marine proxies, which are
fundamentally indirect climatic records, paleosols formed at the
Earth's surface, in direct contact with climatic and environmental
conditions that prevailed at the time of their formation. Potentially
then, paleosol-based proxies could be among the most powerful tools
for reconstructing past environments. Until recently, paleopedology
(the study of paleosols) was largely a qualitative science that relied on
the recognition of features similar to modern soils that allowed for a
“nearest living relative” comparison. That is, a paleosol was identified
as indicating an ancient grassland if it had features similar to a modern
grassland (Fig. 2). This approach still underlies most paleopedology,
but has some fundamental limitations, namely the need for taxonomic
uniformitarianism. Continuing on with the grassland example, the
origin of grasses is most likely in the Cenozoic (e.g., Strömberg, 2002).
However, paleosol-based estimates for the origin of grasslands as
evidenced by Mollisol-like paleosols range from Eocene to Miocene
(Retallack, 1997a,b, 2001a,b) depending on the strictness of one's
taxonomy. Furthermore, others (Terry, 2001) have described Oligocene-age
paleosols as “Mollisols” without meaning to connote that a
grassland ecosystem was present. On the other hand, there are some
types of paleosols found in the Earth's past for which there are
imperfect analogues (e.g., Retallack, 1997c; Sheldon, 2005), or for
which there is no appropriate modern analogue owing to different
environmental and ecological conditions in Earth's past. For example,
weathering at the Earth's surface was occurring in the Precambrian
(e.g., Driese, 2004; Sheldon, 2006b), but under the influence of
microbial enhancement only in the absence of higher plants.
The emergence of new quantitative techniques for reconstructing
various paleoenvironmental and paleoclimatic conditions using
whole rock and isotopic geochemistry has fundamentally changed
the field of paleopedology. Proxies for variables ranging from levissage
to mean annual precipitation to the composition of the paleoatmosphere
at the time of the paleosols' formation have now been
developed. Some of the approaches that we describe in this review
have been widely applied, others have not but could have wider
applicability. We also attempt to “gaze into the crystal ball” to evaluate
Please cite this article as: Sheldon, N.D., Tabor, N.J., Quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols, Earth-
Science Reviews (2009), doi:10.1016/j.earscirev.2009.03.004